There is considerable interest in the identification, isolation and generation of human stem cells. Human stem cells are totipotential or pluripotential precursor cells capable of generating a variety of mature human cell lineages. This ability serves as the basis for the cellular differentiation and specialization necessary for organ and tissue development.
Recent success at transplanting such stem cells have provided new clinical tools to reconstitute and/or supplement bone marrow after myeloablation due to disease, exposure to toxic chemical and/or radiation. Further evidence exists that demonstrates that stem cells can be employed to repopulate many, if not all, tissues and restore physiologic and anatomic functionality. The application of stem cells in tissue engineering, gene therapy delivery and cell therapeutics is also advancing rapidly.
Many different types of mammalian stem cells have been characterized. For example, embryonic stem cells, embryonic germ cells, adult stem cells or other committed stem cells or progenitor cells are known. Certain stem cells have not only been isolated and characterized but have also been cultured under conditions to allow differentiation to a limited extent. A basic problem remains, however, in that obtaining sufficient quantities and populations of human stem cells which are capable of differentiating into all cell types is near impossible. Stem cells are in critically short supply. These are important for the treatment of a wide variety of disorders, including malignancies, inborn errors of metabolism, hemoglobinopathies, and immunodeficiences. It would be highly advantageous to have a source of more embryonic stem cells.
Obtaining sufficient numbers of human stem cells has been problematic for several reasons. First, isolation of normally occurring populations of stem cells in adult tissues has been technically difficult and costly due, in part, to very limited quantity found in blood or tissue. Secondly, procurement of these cells from embryos or fetal tissue, including abortuses, has raised religious and ethical concerns. The widely held belief that the human embryo and fetus constitute independent life has prompted governmental restrictions on the use of such sources for all purposes, including medical research. Alternative sources that do not require the use of cells procured from embryonic or fetal tissue are therefore essential for further progress in the use of stem cells clinically. There are, however, few viable alternative sources of stem cells, particularly human stem cells, and thus supply is limited. Furthermore, harvesting of stem cells from alternative sources in adequate amounts for therapeutic and research purposes is generally laborious, involving, e.g., harvesting of cells or tissues from a donor subject or patient, culturing and/or propagation of cells in vitro, dissection, etc.
For example, Caplan et al. (U.S. Pat. No. 5,486,359 entitled “Human mesenchymal stem cells,” issued Jan. 23, 1996), discloses human mesenchymal stem cell (hMSC) compositions derived from the bone marrow that serve as the progenitors for mesenchymal cell lineages. Caplan et al. discloses that hMSCs are identified by specific cell surface markers that are identified with monoclonal antibodies. Homogeneous hMSC compositions are obtained by positive selection of adherent marrow or periosteal cells that are free of markers associated with either hematopoietic cell or differentiated mesenchymal cells. These isolated mesenchymal cell populations display epitopic characteristics associated with mesenchymal stem cells, have the ability to regenerate in culture without differentiating, and have the ability to differentiate into specific mesenchymal lineages when either induced in vitro or placed in vivo at the site of damaged tissue. The drawback of such methods, however, is that they require harvesting of marrow or periosteal cells from a donor, from which the MSCs must be subsequently isolated.
Hu et al. (WO 00/73421 entitled “Methods of isolation, cryopreservation, and therapeutic use of human amniotic epithelial cells,” published Dec. 7, 2000) discloses human amniotic epithelial cells derived from placenta at delivery that are isolated, cultured, cryopreserved for future use, or induced to differentiate. According to Hu et al., a placenta is harvested immediately after delivery and the amniotic membrane separated from the chorion, e.g., by dissection. Amniotic epithelial cells are isolated from the amniotic membrane according to standard cell isolation techniques. The disclosed cells can be cultured in various media, expanded in culture, cryopreserved, or induced to differentiate. Hu et al. discloses that amniotic epithelial cells are multipotential (and possibly pluripotential), and can differentiate into epithelial tissues such as corneal surface epithelium or vaginal epithelium. The drawback of such methods, however, is that they are labor-intensive and the yield of stem cells is very low. For example, to obtain sufficient numbers of stem cells for typical therapeutic or research purposes, amniotic epithelial cells must be first isolated from the amnion by dissection and cell separation techniques, then cultured and expanded in vitro.
Umbilical cord blood (cord blood) is a known alternative source of hematopoietic progenitor stem cells. Stem cells from cord blood are routinely cryopreserved for use in hematopoietic reconstitution, a widely used therapeutic procedure used in bone marrow and other related transplantations (see e.g., Boyse et al., U.S. Pat. No. 5,004,681, “Preservation of Fetal and Neonatal Hematopoietin Stem and Progenitor Cells of the Blood”, Boyse et al., U.S. Pat. No. 5,192,553, entitled “Isolation and preservation of fetal and neonatal hematopoietic stem and progenitor cells of the blood and methods of therapeutic use”, issued Mar. 9, 1993). Conventional techniques for the collection of cord blood are based on the use of a needle or cannula, which is used with the aid of gravity to drain cord blood from (i.e., exsanguinate) the placenta (Boyse et al., U.S. Pat. No. 5,192,553, issued Mar. 9, 1993; Boyse et al., U.S. Pat. No. 5,004,681, issued Apr. 2, 1991; Anderson, U.S. Pat. No. 5,372,581, entitled Method and apparatus for placental blood collection, issued Dec. 13, 1994; Hessel et al., U.S. Pat. No. 5,415,665, entitled Umbilical cord clamping, cutting, and blood collecting device and method, issued May 16, 1995). The needle or cannula is usually placed in the umbilical vein and the placenta is gently massaged to aid in draining cord blood from the placenta. Thereafter, however, the drained placenta has been regarded as having no further use and has typically been discarded. A major limitation of stem cell procurement from cord blood, moreover, has been the frequently inadequate volume of cord blood obtained, resulting in insufficient cell numbers to effectively reconstitute bone marrow after transplantation.
Naughton et al. (U.S. Pat. No. 5,962,325 entitled “Three-dimensional stromal tissue cultures” issued Oct. 5, 1999) discloses that fetal cells, including fibroblast-like cells and chondrocyte-progenitors, may be obtained from umbilical cord or placenta tissue or umbilical cord blood. Naughton et al. (U.S. Pat. No. 5,962,325) discloses that such fetal stromal cells can be used to prepare a “generic” stromal or cartilaginous tissue. Naughton et al. also discloses that a “specific” stromal tissue may be prepared by inoculating a three-dimensional matrix with fibroblasts derived from a particular individual who is later to receive the cells and/or tissues grown in culture in accordance with the disclosed methods. The drawback of such an approach however, is that it is labor intensive. According to the methods disclosed in Naughton et al., to recover fetal stromal cells from the umbilical cord or placenta requires dissection of these tissues, mincing of the tissue into pieces and disaggregation. Furthermore, to obtain adequate amounts of the fetal stromal cells from umbilical cord blood, as well as the umbilical cord and placenta, requires further expansion ex vivo.
Currently available methods for the ex vivo expansion of cell populations are also labor-intensive. For example, Emerson et al. (Emerson et al., U.S. Pat. No. 6,326,198 entitled “Methods and compositions for the ex vivo replication of stem cells, for the optimization of hematopoietic progenitor cell cultures, and for increasing the metabolism, GM-CSF secretion and/or IL-6 secretion of human stromal cells”, issued Dec. 4, 2001); discloses methods, and culture media conditions for ex vivo culturing of human stem cell division and/or the optimization of human hematopoietic progenitor stem cells. According to the disclosed methods, human stem cells or progenitor cells derived from bone marrow are cultured in a liquid culture medium that is replaced, preferably perfused, either continuously or periodically, at a rate of 1 ml of medium per ml of culture per about 24 to about 48 hour period. Metabolic products are removed and depleted nutrients replenished while maintaining the culture under physiologically acceptable conditions.
Kraus et al. (Kraus et al., U.S. Pat. No. 6,338,942, entitled “Selective expansion of target cell populations”, issued Jan. 15, 2002) discloses that a predetermined target population of cells may be selectively expanded by introducing a starting sample of cells from cord blood or peripheral blood into a growth medium, causing cells of the target cell population to divide, and contacting the cells in the growth medium with a selection element comprising binding molecules with specific affinity (such as a monoclonal antibody for CD34) for a predetermined population of cells (such as CD34 cells), so as to select cells of the predetermined target population from other cells in the growth medium.
Rodgers et al. (U.S. Pat. No. 6,335,195 entitled “Method for promoting hematopoietic and mesenchymal cell proliferation and differentiation,” issued Jan. 1, 2002) discloses methods for ex vivo culture of hematopoietic and mesenchymal stem cells and the induction of lineage-specific cell proliferation and differentiation by growth in the presence of angiotensinogen, angiotensin I (AI), AI analogues, AI fragments and analogues thereof, angiotensin II (AII), AII analogues, AII fragments or analogues thereof or AII AT2 type 2 receptor agonists, either alone or in combination with other growth factors and cytokines. The stem cells are derived from bone marrow, peripheral blood or umbilical cord blood. The drawback of such methods, however, is that such ex vivo methods for inducing proliferation and differentiation of stem cells are time-consuming, as discussed above, and also result in low yields of stem cells.
Naughton et al., (U.S. Pat. No. 6,022,743 entitled “Three-dimensional culture of pancreatic parenchymal cells cultured living stromal tissue prepared in vitro,” issued Feb. 8, 2000) discloses a tissue culture system in which stem cells or progenitor cells (e.g., stromal cells such as those derived from umbilical cord cells, placental cells, mesenchymal stem cells or fetal cells) are propagated on three-dimensional support rather than as a two-dimensional monolayer in, e.g., a culture vessel such as a flask or dish.
Because of restrictions on the collection and use of stem cells, and the inadequate numbers of cells typically collected from cord blood, stem cells are in critically short supply. Stem cells have the potential to be used in the treatment of a wide variety of disorders, including malignancies, inborn errors of metabolism, hemoglobinopathies, and immunodeficiencies. There is a critical need for a readily accessible source of large numbers of human stem cells for a variety of therapeutic and other medically related purposes. The present invention addresses that need and others.